Method and apparatus for operating a clutch in an automated mechanical transmission

ABSTRACT

An apparatus and method for performing a kiss point determining algorithm which is responsive to the approach rate of the release bearing of a clutch for performing the algorithm only under reliable operating conditions. The apparatus includes an electronic controller which sets an approach rate for engaging the clutch in response to the amount of depression of the accelerator pedal of the vehicle by the operator. The amount of engine torque or other engine operating condition is measured and compared against a predetermined magnitude which is indicative of the onset of engagement of the clutch. When an increase of a predetermined magnitude is detected, the accelerator pedal position is compared against a predetermined value. If the accelerator pedal is depressed more than the predetermined value, the kiss point is re-defined as the current location of the release bearing. If the accelerator pedal is not depressed more than the predetermined value, the kiss point is not re-defined.

BACKGROUND OF THE INVENTION

This invention relates in general to vehicle transmissions and in particular to a method and apparatus for automatically controlling the operation of a clutch for use with an automated mechanical transmission in a vehicle drive train assembly.

In virtually all land vehicles in use today, a transmission is provided in a drive train between a source of rotational power, such as an internal combustion or diesel engine, and the driven axle and wheels of the vehicle. A typical transmission includes a case containing an input shaft, an output shaft, and a plurality of meshing gears. Means are provided for connecting selected ones of the meshing gears between the input shaft and the output shaft to provide a desired speed reduction gear ratio therebetween. The meshing gears contained within the transmission case are of varying size so as to provide a plurality of such gear ratios. By appropriately shifting among these various gear ratios, acceleration and deceleration of the vehicle can be accomplished in a smooth and efficient manner.

To facilitate the operation of the transmission, it is well known to provide a clutch between the vehicle engine and the transmission. When the clutch is engaged, the transmission is driven by the vehicle engine to operate the vehicle at a selected gear ratio. To shift the transmission from a first gear ratio to a second gear ratio, the clutch is initially disengaged such that power is not transmitted from the vehicle engine to the transmission. This allows the gear shifting operation to occur within the transmission under a non-torque loading condition to prevent undesirable clashing of the meshing gear teeth. Thereafter, the clutch is re-engaged such that power is transmitted from the vehicle engine to the transmission to operate the vehicle at the second gear ratio.

A typical structure for a vehicle clutch includes a cover which is connected to a flywheel secured to the end of the output shaft of the vehicle engine for rotation therewith. A pressure plate is disposed within the clutch between the cover and the flywheel. The pressure plate is connected for rotation with the flywheel and the cover, but is permitted to move axially relative thereto. Thus, the flywheel, the cover, and the pressure plate are all constantly rotatably driven by the vehicle engine. Between the flywheel and the pressure plate, a driven disc assembly is disposed. The driven disc assembly is supported on the input shaft of the transmission for rotation therewith, but is permitted to move axially relative thereto. To engage the clutch, the pressure plate is moved axially toward the flywheel to an engaged position, wherein the driven disc assembly is frictionally engaged between the flywheel and the pressure plate. As a result, the driven disc assembly (and the input shaft of the transmission upon which it is supported) are driven to rotate with the flywheel, the cover, and the pressure plate. To disengage the clutch, the pressure plate is moved axially away from the flywheel to a disengaged position. When the pressure plate is moved axially to this disengaged position, the driven disc assembly is not frictionally engaged between the flywheel and the pressure plate. As a result, the driven disc assembly (and the input shaft of the transmission upon which it is supported) are not driven to rotate with the flywheel, the cover, and the pressure plate.

To effect such axial movement of the pressure plate between the engaged and disengaged positions, most vehicle clutches are provided with a release assembly including a generally hollow cylindrical release sleeve which is disposed about the output shaft of the clutch. The forward end of the release sleeve extends within the clutch and is connected through a plurality of levers or other mechanical mechanism to the pressure plate. In this manner, axial movement of the release sleeve causes corresponding axial movement of the pressure plate between the engaged and disengaged positions. Usually, one or more engagement springs are provided within the clutch to urge the pressure plate toward the engaged position. The engagement springs typically react between the release sleeve and the cover to normally maintain the clutch in the engaged condition. The rearward end of the release sleeve extends outwardly from the clutch through a central opening formed through the cover. Because the release sleeve is connected to the cover and the pressure plate of the clutch, it is also constantly driven to rotate whenever the vehicle engine is operating. Thus, an annular release bearing is usually mounted on the rearward end of the release sleeve. The release bearing is axially fixed on the release sleeve and includes an inner race which rotates with release sleeve, an outer race which is restrained from rotation, and a plurality of bearings disposed between the inner race and the outer race to accommodate such relative rotation. The non-rotating outer race of the release bearing is typically engaged by an actuating mechanism for moving the release sleeve (and, therefore, the pressure plate) between the engaged and disengaged positions to operate the clutch.

In a conventional mechanical transmission, both the operation of the clutch and the gear shifting operation in the transmission are performed manually by an operator of the vehicle. For example, the clutch can be disengaged by depressing a clutch pedal located in the driver compartment of the vehicle. The clutch pedal is connected through a mechanical linkage to the outer race of the release bearing of the clutch such that when the clutch pedal is depressed, the pressure plate of the clutch is moved from the engaged position to the disengaged position. When the clutch pedal is released, the engagement springs provided within the clutch return the pressure plate from the disengaged position to the engaged position. Similarly, the gear shifting operation in the transmission can be performed when the clutch is disengaged by manually moving a shift lever which extends from the transmission into the driver compartment of the vehicle. Manually operated clutch/transmission assemblies of this general type are well known in the art and are relatively simple, inexpensive, and lightweight in structure and operation. Because of this, the majority of medium and heavy duty truck clutch/transmission assemblies in common use today are manually operated.

More recently, however, in order to improve the convenience of use of manually operated clutch/transmission assemblies, various structures have been proposed for partially or fully automating the shifting of an otherwise manually operated transmission. In a partially or fully automated manual transmission, the driver-manipulated clutch pedal may be replaced by an automatic clutch actuator, such as a hydraulic or pneumatic actuator. The operation of the automatic clutch actuator can be controlled by an electronic controller or other control mechanism to selectively engage and disengage the clutch without manual effort by the driver. Similarly, the driver-manipulated shift lever may also be replaced by an automatic transmission actuator, such as a hydraulic or pneumatic actuator which is controlled by an electronic controller or other control mechanism to select and engage desired gear ratios for use.

In both manually operated transmissions and in partially or fully automated manual transmissions, one of the most difficult operations to perform is to initially launch the vehicle from at or near a stand-still. This is because the force required to overcome the inertia of the vehicle is the greatest when attempting to initially accelerate the vehicle from at or near zero velocity. This relatively large amount of inertial force results in a relatively large load being placed on the vehicle engine when the clutch is engaged during a vehicle launch. Thus, the movement of the release bearing from the disengaged position to the engaged position must be carefully controlled during the initial launch of the vehicle to prevent the engine from stalling and to avoid undesirable sudden jerking movement of the vehicle. Although the same considerations are generally applicable when re-engaging the clutch during subsequent shifting operations in the higher gear ratios of the transmissions, the control of the movement of the release bearing from the disengaged position to the engaged position has been found to be less critical when shifting among such higher gear ratios because a much lesser force is required to overcome the inertia of the vehicle when the vehicle is already moving.

To address these considerations, the total movement of the release bearing from the disengaged position to the engaged position can be divided into three ranges of movement. The first range of movement is from the disengaged position to a first intermediate position (referred to as the transition point). The transition point is selected to be relatively near, but spaced apart from, the position of the release bearing at which the driven disc assembly of the clutch is initially engaged by the flywheel and the pressure plate. Thus, during this first range of movement (referred to as the transition movement), the clutch is completely disengaged, and no torque is transmitted through the clutch to the transmission. The second range of movement is from the transition point to a second intermediate position (referred to as the kiss point). The kiss point is the position of the release bearing at which the driven disc assembly is initially engaged by the flywheel and the pressure plate. Thus, during this second range of movement (referred to as the approach movement) from the transition point to the kiss point, the clutch is disengaged until the release bearing reaches the kiss point, at which point the first measurable amount of torque is transmitted through the clutch to the transmission. The third range of movement of the release bearing is from the kiss point to the engaged position. The engaged position is the position of the release bearing at which the driven disc assembly is completely engaged by the flywheel and the pressure plate. Thus, during this third range of movement (referred to as the engagement movement), the clutch is gradually engaged so as to increase the amount of torque which is transmitted through the clutch to the transmission from the first measurable amount at the kiss point to the full capacity of the clutch at the engaged position.

As mentioned above, during the initial transition movement of the release bearing from the disengaged position to the transition point, the clutch is completely disengaged. Thus, it is desirable that the speed of the transition movement of the release bearing (referred to as the transition rate) be as large as possible to minimize the time duration of the gear shifting operation. Because the clutch is completely disengaged during this transition movement, the movement of the release bearing from the disengaged position to the transition point need not be carefully controlled to prevent the engine from stalling and to avoid undesirable sudden jerking movement of the vehicle. Similarly, during the approach movement of the release bearing from the transition point to the kiss point, the clutch is disengaged until the release bearing reaches the kiss point. Thus, it is also desirable that speed of the approach movement of the release bearing (referred to as the approach rate) be as large as possible to minimize the time duration of the gear shifting operation. After the kiss point has been reached, however, it is desirable that the speed of engagement movement of the release bearing (referred to as the engagement rate) be somewhat smaller than the approach rate to prevent the engine from stalling and to avoid undesirable sudden jerking movement of the vehicle. Thus, to optimize the engagement of the clutch, the movement of the release bearing of the clutch will decelerate from the relatively faster approach rate to the relatively slower engagement rate when the release bearing is moved through the kiss point.

To accomplish this effectively, it is important to properly ascertain the location of the kiss point so that the electronic controller can decelerate the movement of the release bearing at the proper point in the engagement process. Unfortunately, it has been found that the precise location of the kiss point will vary during use in response to many factors, such as temperature, mechanical wear, and the like. To optimize the operation of the clutch, it would be desirable to determine the actual position of the kiss point each time the clutch is engaged. A number of kiss point determining algorithms are known in the art. Typically, the kiss point is determined by measuring an increase in torque (or a change an another engine operating condition) at the output shaft of the engine, indicating the onset of clutch engagement. However, it has been found that the accuracy of such kiss point determining algorithms is dependent upon the approach rate of the release bearing. Specifically, it has been found that known kiss point determining algorithms are not sufficiently accurate if performed when the approach rate of the release bearing is less than a predetermined speed. If the approach rate is relatively fast, the resulting increase in torque will occur relatively fast, thus facilitating a precise measurement of the kiss point. If, on the other hand, the approach rate is relatively slow, the resulting increase in torque will occur relatively slow, thus inhibiting a precise measurement of the kiss point. Thus, it would be desirable to provide an apparatus and method for performing a kiss point determining algorithm which is responsive to the approach rate of the release bearing of a clutch in order to insure that a determination of the kiss point is made only under reliable operating conditions.

SUMMARY OF THE INVENTION

This invention relates to an apparatus and method for performing a kiss point determining algorithm which is responsive to the approach rate of the release bearing of a clutch for performing the algorithm only under reliable operating conditions. The apparatus includes an electronic controller which sets an approach rate for engaging the clutch in response to the amount of depression of the accelerator pedal of the vehicle by the operator. The amount of engine torque or other engine operating condition is measured and compared against a predetermined magnitude which is indicative of the onset of engagement of the clutch. When an increase of a predetermined magnitude is detected, the accelerator pedal position is compared against a predetermined value. If the accelerator pedal is depressed more than the predetermined value, the kiss point is re-defined as the current location of the release bearing. If the accelerator pedal is not depressed more than the predetermined value, the kiss point is not re-defined.

Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a vehicle drive train assembly including an electronic controller in accordance with this invention.

FIG. 2 is sectional elevational view of the clutch actuator and portions of the clutch and transmission illustrated in FIG. 1 showing the clutch actuator and the clutch in a disengaged position, together with a block diagram of the valves and related control circuitry for operating the clutch actuator and the clutch.

FIG. 3 is a flow chart of an algorithm for controlling the movement of the release bearing of the clutch in its approach movement from the transition point to the kiss point.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, there is illustrated in FIG. 1 a block diagram of a vehicle drive train assembly, indicated generally at 10. The drive train assembly 10 includes a conventional engine 11 or other source of rotational power. The engine 11 is connected through an output shaft 11 a, such as a crankshaft of the engine 11, to a clutch 12. The clutch 12 is also conventional in the art and functions to selectively connect the output shaft 11 a of the engine 11 to an input shaft 13 a of a transmission 13. The transmission 13 contains a plurality of meshing gears (not shown) which are selectively connected between the input shaft 13 a and an output shaft 13 b. The meshing gears contained within the transmission 13 are of varying size so as to provide a plurality of such gear ratios. By appropriately shifting among these various gear ratios, a desired speed reduction gear ratio can be provided between the input shaft 13 a and the output shaft 13 b. Consequently, acceleration and deceleration of the vehicle can be accomplished in a smooth and efficient manner. The output shaft 13 b is connected to a conventional axle assembly 14. The axle assembly 14 includes one or more wheels which are rotatably driven by the engine 11 whenever the clutch 12 and the transmission 13 are engaged. This general structure for the drive train assembly 10 is well known in the art.

The illustrated transmission 13 may be either a partially or filly automated mechanical transmission. In a typical partially automated manual transmission, a driver-manipulated shift lever (not shown) engages and moves certain ones of a plurality of shift rails contained within the transmission to engage a first set of gear ratios for use. However, an automatically shifting transmission actuator 15 is provided on the transmission 13 to engage and move the remaining shift rails to engage a second set of gear ratios for use. For example, it is known to provide a partially automated manual transmission wherein the lower gear ratios are manually selected and engaged by the vehicle driver using the shift lever, while the higher gear ratios are automatically selected and engaged by the transmission actuator 15. One example of a typical partially automated manual transmission of this general structure is disclosed in detail in U.S. Pat. No. 5,450,767, owned by the assigned of this application. The disclosure of that patent is incorporated herein by reference. In a fully automated manual transmission, the driver-operated shift lever is usually replaced by the transmission actuator 15. The transmission actuator 15 functions to shift all of the shift rails contained within the transmission so as to select and engage all of the available gear ratios. The above-referenced patent discusses the adaptability of the disclosed partially automated transmission actuator 15 to fully automate the shifting of the transmission disclosed therein.

To facilitate the automatic shifting of the transmission 15, the clutch 12 is provided with a clutch actuator 16. The structure and operation of the clutch actuator 16 will be discussed further below. Briefly, however, the clutch actuator 16 is provided to replace a driver-manipulated clutch pedal so as to partially or fully automate the operation of the clutch 12. The clutch actuator 16 is effective to operate the clutch 12 in either an engaged or disengaged mode. When the clutch 12 is engaged, the transmission 13 is driven by the vehicle engine 11 to operate the vehicle at a selected gear ratio. To shift the transmission 13 from a first gear ratio to a second gear ratio, the clutch 12 is initially disengaged such that power is not transmitted from the vehicle engine 11 to the transmission 13. This allows the transmission actuator 15 to effect a gear shifting operation within the transmission 13 under a non-torque loading condition to prevent undesirable clashing of the meshing gear teeth. Thereafter, the clutch 12 is re-engaged such that power is transmitted from the vehicle engine 11 to the transmission 13 to operate the vehicle at the second gear ratio.

The operation of the clutch actuator 16 and the transmission actuator 15 are controlled by an electronic controller 20. The electronic controller 20 can be embodied as any conventional microprocessor or similar computing apparatus which can be programmed to operate the clutch actuator 16 (to effect automatic disengagement and engagement of the clutch 12) and the transmission actuator 15 (to effect automatic shifting of the transmission 13 when the clutch 12 is disengaged) as described above. The operation of the electronic controller 20 will be described in detail below. A transmission output shaft speed sensor 21 provides an input signal to the electronic controller 20. The transmission output shaft speed sensor 21 is conventional in the art and is adapted to generate an electrical signal which is representative of the actual rotational speed of the output shaft 13 b of the transmission 13. A clutch position sensor 22 also provides an input signal to the electronic controller 20. The structure and operation of the clutch position sensor 22 will be described below.

An engine controller 23 is provided to control the operation of the vehicle engine 11. The engine controller 23 can also be embodied as any conventional microprocessor or similar computing apparatus which can be programmed to operate the engine 11 in a desired manner. Primarily, the engine controller 23 controls the operation of the engine 11 in response to an input signal generated by an accelerator pedal position sensor 24. The accelerator pedal position sensor 24 is conventional in the art and is adapted to generate an electrical signal which is representative of the actual position of the accelerator pedal (not shown) of the vehicle. As is well known, the accelerator pedal is physically manipulated by the foot of the driver of the vehicle to control the operation thereof The accelerator pedal is depressed by the driver when it is desired to increase the speed of the engine 11 and move the vehicle. Conversely, the accelerator pedal is released when it is desired to decrease the speed of the engine 11 to slow or stop such movement of the vehicle. Thus, the engine controller 23 controls the speed of the engine 11 in response to the signal from the accelerator pedal position sensor 24 so as to operate the vehicle as desired by the driver. The accelerator pedal position sensor 24 may, if desired, be replaced by a throttle position sensor (not shown) or other driver-responsive sensor which generates a signal which is representative of the desired speed or mode of operation of the vehicle. A second input to the engine controller 23 is an engine output shaft speed sensor 25. The engine output shaft speed sensor 25 is conventional in the art and is adapted to generate an electrical signal which is representative of the actual rotational speed of the output shaft 11 a of the engine 11.

The electronic controller 20 and the engine controller 23 communicate with one another over a data bus line 26 extending therebetween. In a manner which is generally conventional in the art, the electronic controller 20 and the engine controller 23 are programmed to communicate and cooperate with one another to so as to control the operation of the vehicle in a manner desired by the driver of the vehicle. Specifically, the electronic controller 20 and the engine controller 23 are effective to control the operation of the engine 11, the clutch 12, and the transmission 13 in such a manner that the vehicle can be started and stopped solely by physical manipulation of the accelerator and brake pedals, similar to a conventional automatic transmission in a passenger car. To accomplish this, the signals from the accelerator pedal position sensor 24 and the engine output shaft speed sensor 25 are available to the electronic controller 20 over the data bus line 26. Alternatively, the signals from the accelerator pedal position sensor 24 and the engine output shaft speed sensor 25 can be fed directly to the electronic controller 20.

Referring now to FIG. 2, the clutch actuator 16 and portions of the clutch 12 and the transmission 13 are illustrated in detail. The structure and operation of the clutch actuator 16 are disclosed and illustrated in detail in co-pending application Ser. No. 08/775,460, filed Dec. 30, 1996 (owned by the assigned of this invention), the disclosure of which is incorporated herein by reference. Briefly, however, the clutch actuator 16 includes an outer cylinder housing 30, a hollow cylindrical piston 31, and an inner cylinder housing 32. The piston 31 has at least one, and preferably a plurality, of axially forwardly projecting protrusions 31 a, each of which has a circumferentially extending groove 31b formed therein. To assemble the clutch actuator 16, the piston 31 is initially disposed concentrically within the outer cylinder housing 30, and the inner cylinder housing 32 is disposed concentrically within the piston 31. Then, the outer cylinder housing 30 is secured to a forwardly facing surface of a case of the transmission 13 by threaded fasteners (not illustrated) or other means. When this is done, a forwardly facing surface 32 a of the inner cylinder housing 32 abuts a complementary shaped, rearwardly facing annular surface 30 a formed within the outer cylinder housing 30. At the same time, a rearwardly facing surface 30 b of the outer cylinder housing 30 abuts portions of the case of the transmission 13. Thus, the inner cylinder housing 32 is captured between the case of the transmission 13 and the outer cylinder housing 30 so as to be fixed in position relative thereto. At the same time, a circumferential rim portion 31 c of the piston 31 is received in an undercut 30 c formed in the interior of the outer cylinder housing 30. Thus, the piston 31 is capable of limited axial movement relative to the outer cylinder housing 30 and the inner cylinder housing 32.

The clutch 12 is a conventional pull-to-release type clutch and includes a cover 12 a which is connected to a flywheel (not illustrated) which, in turn, is connected to the output shaft 11 a of the engine 11. The flywheel and the cover 12 a are thus rotatably driven by the engine 11 of the vehicle for rotation about an axis. The cover 12 a has a central opening formed therethrough which receives a hollow, generally cylindrical release sleeve 12 b. The release sleeve 12 b is disposed concentrically about the transmission input shaft 13 a. A driven disc assembly (not shown) is mounted within the clutch 12 on the forward end of the transmission input shaft 13 a for rotation therewith and for axial movement relative thereto. When the clutch 12 is engaged, torque is transmitted from the driven disc assembly to the transmission input shaft 13 a in a known manner. When the clutch 12 is disengaged, no torque is transmitted from the driven disc assembly to the transmission input shaft 13 a.

A forward end of the release sleeve 12 b has an annular groove formed thereabout which receives the radially innermost ends of a plurality of clutch operating levers 12 c therein. Thus, axial movement of the release sleeve 12 b causes pivoting movement of the clutch operating levers 12 c which, in turn, causes engagement and disengagement of the clutch 12 in a known manner. A plurality of clutch engagement springs 12 d (only one of which is illustrated) reacts between the cover 12 a and the forward end of the release sleeve 12 b. The ends of the clutch engagement springs 12 d are preferably supported on respective seats provided on the release sleeve 12 b and the cover 12 a. The springs 12 d urge the release sleeve 12 b axially forwardly (toward the left when viewing FIG. 2) toward an engaged position, wherein the components of the clutch 12 are frictionally engaged so as to cause the transmission input shaft 13 a to be rotatably driven by the engine 11. When the release sleeve 12 b is moved axially rearwardly (toward the right when viewing FIG. 2) against the urging of the engagement springs 12 d toward a disengaged position, the components of the clutch 12 are frictionally disengaged so as to prevent the transmission input shaft 13 a from being rotatably driven by the engine 11.

The rearward end of the release sleeve 12 b extends axially rearwardly through the central opening in the cover 12 a. An annular release bearing 33 is disposed about the rearward end of the release sleeve 12 b and is retained on one side by a snap ring 34 disposed within an annular groove. A retaining ring 35 is also disposed about the rearward end of the release sleeve 12 b adjacent to the forward side of the release bearing 33. A snap ring 36 is disposed in an annular groove in the release sleeve 12 b to retain the retaining ring 35 on the release sleeve 12 b. Thus, the release bearing 33 and the retaining ring 35 are secured to the release sleeve 12 b for axial movement therewith. A snap ring 37 is disposed within the groove formed in the outer surface of the retaining ring 35. The snap ring 37 connects the piston 31 with the retaining ring 35 such that axial movement of the piston 31 causes corresponding axial movement of the retaining ring 35, the release bearing 33, and the release sleeve 12 b.

An annular chamber 38 is defined between the outer surface of the body of the piston 31, the enlarged rim portion 31 c formed at the rearward end of the piston 31, and the undercut 30 c formed in the inner surface of the outer cylinder housing 30. The chamber 38 is sealed to form a fluid-tight chamber by sealing elements, such as O-rings. A radially extending port 39 is formed through the outer cylinder housing 30. As will be explained in detail below, pressurized fluid (hydraulic or pneumatic, as desired) is supplied through the port 39 used to effect axial movement of the piston 31 in one direction relative to the outer cylinder housing 30 and the inner cylinder housing 31.

The clutch position sensor 22 is mounted on the outer cylinder housing 30 for generating an electrical signal which is representative of the axial position of the piston 31 relative to the outer and inner cylinder housings 30 and 32. Such an electrical position signal is used by an electronic controller 20 for automatically operating the clutch actuator 16 in a manner described in detail below. The clutch position sensor 22 is conventional in the art.

The port 39 communicates through a conduit 40 with an engage valve 41 and a disengage valve 42. The engage valve 41 communicates with a reservoir (in hydraulic systems) or the atmosphere (in pneumatic systems), while the disengage valve 42 communicates with a source of pressurized fluid 43, either hydraulic or pneumatic as desired. The operation of the engage valve 41 is controlled by an engage solenoid 44, while the operation of the disengage valve 42 is controlled by a disengage solenoid 45. The engage solenoid 44 and the disengage solenoid 45 are, in turn, connected to the electronic controller 23 so as to be selectively operated thereby.

The clutch 12 is normally maintained in the engaged position under the influence of the engagement springs 12 d. When it is desired to disengage the clutch 12, the engage solenoid 44 is actuated by the electronic controller 20 to close the engage valve 41, and the disengage solenoid 45 is actuated by the electronic controller 20 to open the disengage valve 42. As a result, pressurized fluid from the source 43 is supplied to the chamber 38, causing the piston 31 to move rearwardly (toward the right when viewing FIG. 2) against the urging of the engagement springs 12 d. As discussed above, such rearward movement of the piston 31 causes the clutch 12 to be disengaged. For several reasons which are well known in the art, the disengage valve 42 is operated by the electronic controller 20 in an on-off manner, i.e., either wide open or completely closed.

When it is desired to subsequently re-engage the clutch 12, the engage solenoid 44 is actuated by the electronic controller 20 to open the engage valve 41, and the disengage solenoid 45 is actuated by the electronic controller 20 to close the disengage valve 42. As a result, the chamber 38 is vented to the reservoir, causing the piston 31 to move forwardly (toward the left when viewing FIG. 2) under the influence of the engagement springs 12 d. As discussed above, such forward movement of the piston 31 causes the clutch 12 to be engaged. For several reasons which are well known in the art, the engage valve 44 is operated using pulse width modulation techniques to control the engagement of the clutch 12. The electronic controller 20 varies the duty cycle of the pulse width modulation of the engage valve 41 so as to adjust the rate at which the pressurized fluid in the chamber 38 is vented to the reservoir. By adjusting the rate of venting of the chamber 38 in this manner, the speed at which the release bearing 33 is moved from the disengaged position to the engaged position can be precisely controlled. Precise control of the speed of movement of the release bearing from the disengaged position to the engaged position is important to engage the clutch 12 smoothly and avoid undesirable sudden jerking movement of the vehicle.

As discussed above, the total movement of the release bearing 33 from the disengaged position to the engaged position can be divided into three ranges of movement. The first range of movement of the release bearing 33 is from the disengaged position to a first intermediate position (referred to as the transition point). The transition point is selected to be relatively near, but spaced apart from, the position of the release bearing 33 at which the driven disc assembly of the clutch 12 is initially engaged by the flywheel and the pressure plate. Thus, during this first range of movement (referred to as the transition movement), the clutch 12 is completely disengaged, and no torque is transmitted through the clutch 12 to the transmission 13. The second range of movement of the release bearing 33 is from the transition point to a second intermediate position (referred to as the kiss point). The kiss point is the position of the release bearing 33 at which the driven disc assembly is initially engaged by the flywheel and the pressure plate. Thus, during this second range of movement (referred to as the approach movement) from the transition point to the kiss point, the clutch 12 is disengaged until the release bearing 33 reaches the kiss point, at which point the first measurable amount of torque is transmitted through the clutch 12 to the transmission 13. The third range of movement of the release bearing 33 is from the kiss point to the engaged position. The engaged position is the position of the release bearing 33 at which the driven disc assembly is completely engaged by the flywheel and the pressure plate. Thus, during this third range of movement (referred to as the engagement movement), the clutch 12 is gradually engaged so as to increase the amount of torque which is transmitted through the clutch 12 to the transmission 13 from the first measurable amount at the kiss point to the full capacity of the clutch 12 at the engaged position.

Movement of the release bearing 33 through the initial transition range of movement can be accomplished in any known manner. As suggested above, the transition movement of the release bearing 33 from the disengaged position to the transition point can be accomplished by pulse width modulating the engage valve 41 at a predetermined duty cycle so as to cause rapid movement of the release bearing 33 from the disengaged position to the transition point. To accomplish this, the engage valve 41 may be pulse width modulated at a constant rate throughout the transition movement of the release bearing 33. Alternatively, the engage valve 41 may be pulse width modulated at a rate which varies with the current position of the release bearing 33 relative to the transition point so as to decelerate the release bearing 33 somewhat as it approaches the transition point. The electronic controller 20 can be programmed to monitor the clutch position signal from the clutch position sensor 22 to determine when the release bearing 33 has reached the transition point. Regardless of the specific transition rate which is used, it is desirable that the initial transition movement of the release bearing 33 be performed as rapidly as possible because the clutch 12 is completely disengaged throughout. Therefore, no sudden and undesirable engagement of the clutch 12 will occur during this initial transition movement of the release bearing 33.

The algorithm of this invention relates to the control of the movement of the release bearing 33 in its approach movement from the transition point to the kiss point. Referring now to FIG. 3, there is illustrated a flow chart of an algorithm 90 for controlling the movement of the release bearing 33 of the clutch 12 in its approach movement from the transition point to the kiss point. In the first step 91 of the algorithm 90, the electronic controller 20 reads the accelerator pedal position signal PED_(POS) from the engine controller 23. Then, the algorithm 90 enters a step 92 wherein the electronic controller 20 sets the approach rate. Any desired approach rate may be set by the electronic controller 20. For example, the approach rate may be set as being equal to the sum of a predetermined minimum start rate and a factor related to the magnitude of the accelerator pedal position signal PED_(POS). In the next step 93, the electronic controller 20 actuates the engage valve 41 and the disengage valve 42 (by means of the respective solenoids 44 and 45) to effect movement of the release bearing 33 of the clutch 12 according to the calculated approach rate. Thus, the clutch engagement process is continued from the transition point.

In the next step 94 of the algorithm 90, the electronic controller 20 reads the engine torque signal generated by the engine controller 23 to the engine 11 over the data bus line 26. The algorithm 90 next enters a first decision point 95 wherein the engine torque signal is compared with a first constant value K1. The first constant value K1 is selected to represent a predetermined amount of torque generated by the engine 11. As mentioned above, the kiss point is the position of the release bearing 33 at which the first measurable amount of torque is transmitted through the clutch 12 to the transmission 13. To accommodate this transmission of torque without stalling, the engine controller 23 increases the engine torque signal to the engine 11. Thus, if the engine torque signal is less than the first constant value K1, then it is assumed that the release bearing 33 has not yet reached the kiss point. In that instance, the algorithm 90 branches from the first decision point 95 back to the step 91 wherein the electronic controller 20 again reads the accelerator pedal position signal PED_(POS) from the engine controller 23. This loop in the algorithm 90 continues until the engine torque signal is greater than or equal to the first constant value K1.

When this occurs, it is assumed that the release bearing 33 of the clutch 12 has reached the kiss point. Thus, the algorithm 90 branches from the decision point 95 to a second decision point 96 wherein the accelerator pedal position signal PED_(POS) is compared with a second constant value K2. The second constant value K2 is selected to represent a relatively large amount of depression of the accelerator pedal, such as more than halfway depressed. If the accelerator pedal position signal PED_(POS) is less than or equal to the second constant value K2, then it can be assumed that the approach rate is too slow to insure that a determination of the kiss point will be made under reliable operating conditions. Thus, the algorithm 90 branches from the second decision point 96 to a step 97 wherein the engagement rate is set to complete the engagement process.

If, on the other hand, the accelerator pedal position signal PED_(POS) is greater than the second constant value K2, then it can be assumed that the approach rate is fast enough to insure that a determination of the kiss point will be made under reliable operating conditions. Thus, the algorithm 90 branches from the second decision point 96 to a step 98 wherein the electronic controller 20 reads the actual position CLT_(POS) of the release bearing 33 of the clutch 12 from the clutch position sensor 22. As discussed above, the clutch position sensor 22 is adapted to generate an electrical signal which is representative of the axial position of the piston 31 relative to the outer and inner cylinder housings 30 and 32 and, therefore, the actual position of the release bearing 33. Next, the algorithm 90 enters a step 99 wherein the kiss point is set to be equal to the actual position CLT_(POS) of the release bearing 33. Lastly, the algorithm 90 enters the step 97 wherein the engagement rate is set to complete the engagement process. Thus, it will be appreciated that the kiss point is updated only when the approach rate (as determined by the amount of depression of the accelerator pedal) is greater than a predetermined value.

As described above, the algorithm 90 updates the location of the kiss point whenever both (1) the kiss point is reached, as determined by the first decision point 95, and (2) the accelerator pedal position signal PED_(POS) is greater than the second constant value K2, as determined by the second decision point 96. It may be desirable to modify the algorithm 90 such that the location of the kiss point is updated only when the amount of depression of the accelerator pedal is greater than the second constant value K2 not only when the kiss point has been detected, but throughout the entire approach movement of the release bearing 33. To accomplish this, the algorithm 90 may be modified such that the electronic controller 20 compares the accelerator pedal position signal PED_(POS) with the second constant value K2 each time it loops back to the step 91 during the approach movement. If the amount of depression of the accelerator pedal is less than or equal to the second constant value K2 at any point during the approach movement of the release bearing 33, then the engagement process is completed without updating the location of the kiss point. Similarly, the algorithm 90 may be modified to include monitoring the accelerator pedal position signal PED_(POS) throughout the transition movement of the release bearing 33, or throughout both the transition and approach movements of the release bearing 33 to insure that a determination of the kiss point will be made under reliable operating conditions.

Movement of the release bearing 33 at the engagement rate through the third range of movement can be accomplished in any known manner. As suggested above, the clutch 12 is gradually engaged during the engagement movement of the release bearing 33 from the kiss point to the engaged position to prevent the engine from stalling and avoid undesirable sudden jerking movement of the vehicle. The electronic controller 20 can be programmed to automatically alter the duty cycle of the engage valve during this engagement movement of the release bearing 33 in response to sensed operating conditions. For example, the electronic controller 20 can be responsive to the amount of depression of the accelerator pedal from the pedal position sensor 24 and the engine speed for adjusting the duty cycle of the engage valve. However, any known algorithm may be used to control the movement of the release bearing 33 in its final engagement movement from the kiss point to the engaged position to insure that a determination of the kiss point will be made under reliable operating conditions.

Although this invention has been described in terms of monitoring engine torque as an indicator of the onset of clutch engagement, it will be appreciated that other engine operating conditions or parameters may be used to detect the kiss point. For example, engine load will increase at the onset of clutch engagement, while engine speed will decrease at the onset of clutch engagement. This invention contemplates the use of any engine operating condition or other parameter to detect the kiss point.

In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope. 

What is claimed is:
 1. An apparatus for controlling an approach rate of a clutch having an input member and an output member for selectively connecting an engine to a transmission in a vehicle having an accelerator pedal, the apparatus comprising: a sensor for generating a signal which is representative of an operating condition of the engine; a sensor for generating a signal which is representative of the approach rate of the clutch; a controller for generating control signal which is representative of an approach rate of the clutch, said controller being responsive to a predetermined change in said engine operating condition sensor signal for determining a kiss point during the engagement of the clutch only when the signal representative of the approach rate of the clutch is greater than a predetermined value; and a clutch actuator for controlling the approach rate of the clutch in response to said control signal. 